1. Field of the Invention
The object of the present invention is a lighting or signaling device equipping a motor vehicle, comprising at least one optical guide able to produce diffusion of the light over at least part of its length. The invention also concerns a vehicle comprising such a lighting or signaling device.
2. Description of the Related Art
In the field of motor vehicle lighting and signaling, optical guides are being used more and more frequently. An optical guide is, very schematically, an elongate element made from transparent material, generally in the form of a cylinder. Close to one of the ends of the guide, referred to as the guide entry face, one (or more) light source is disposed, for example a small light source of the light emitting diode type: the light rays emitted by this source propagate by total reflection in the length of the guide in the direction of its opposite end, referred to as the end face of the guide. Some of the light rays propagating in the guide will emerge from it in the so-called front face of the guide by virtue of the presence of reflecting elements disposed on the so-called rear face of the guide, opposite to the previous one. These reflecting elements consist for example of prisms. The guide thus emits light over its entire length. It has the advantage of being able to take very varied geometric forms, be it rectilinear or in an arc of a circle, and bring an illuminating surface even into areas of the vehicle headlight or light that are not very accessible. It thus participates greatly in the style of the headlight or light. However, existing light guides are open to improvement: this is because it is often tricky to ensure an identical illumination level between the first and second ends of the guide, particularly if it has a significant length, the illumination level having a tendency to decrease on moving away from the entry face of the guide. Moreover, it is also tricky to ensure a homogeneous appearance to the guide whatever the angle of vision that there is of the guide, the light emerging from the guide having an angular distribution that is often insufficiently broad. However, it is an important point according to the arrangement of the guide and its shape inside the headlight or light: there is a tendency to design the guide so that it illuminates mainly in the axis of the vehicle in order to meet photometric standards. However, it also proves important to have a homogeneous and visually agreeable illuminated appearance also when the observer moves away from the longitudinal axis of the vehicle. It may also be wished to improve the optical efficiency of the guide since there may be leakages of light therein lost through the rear face of the guide in particular.
It is already known from the patent EP 1 443 265 how to associate a light guide with a reflector situated at the rear of the light guide in order best to limit the leakages of light and thus improve the optical efficiency of the guide.
The aim of the invention is then to obtain an improved light guide that makes it possible in particular to have a more homogeneous illuminated appearance, particularly in a wide range of vision angles of incidence.